What are the MTG Commander color identity rules and how do they impact deck building strategies?

In MTG Commander, each deck has a color identity based on the colors of the cards in the deck. A card's color identity includes all colors in its mana cost and any color symbols in its rules text. Players can only include cards in their deck that match the color identity of their commander. This rule impacts deck building strategies by limiting the cards that can be included, requiring players to carefully choose cards that work well together within the color identity of their commander.